The role of 18F-fluorodeoxyglucose positron emission tomography/computed tomography whole body imaging in the evaluation of focal thyroid incidentaloma.

Background: 18F-fluorodeoxyglucose positron emission tomography/computed tomography (18F-FDG PET/CT) is a non-invasive whole-body imaging technique used to evaluate various types of malignancies. Recent advances have rapidly developed it into a diagnostic imaging tool in oncology.

Objective: In this study, the prevalence of thyroid incidentaloma and its cancer risk rate were investigated by 18F-FDG PET/CT. The threshold of maximal standardized uptake value (SUVmax) for differentiation of benign and malignant tumors was also defined.

Methods: From June 2007 to December 2008, 3600 subjects underwent 18F-FDG PET/CT in our department. Among the population under study, 115 subjects developed focal increased 18F-FDG uptake as thyroid incidentalomas and their SUVmax were analyzed qualitatively and semi-quantitatively.

Results: Data from the 18F-FDG PET/CT study suggested that overall prevalence of thyroid incidentaloma was 3.2% (115/3580). Among the 96 incidentalomas (20 confirmed by surgery; 76 confirmed by fine-needle aspiration) with additional cyto- and histopathological diagnoses, 50% were malignant thyroid lesions. Therefore, the cancer risk of thyroid incidentaloma was 50%. SUVmax values of the malignant samples were significantly higher than those of benign (p=0.00, p<0.05). A SUVmax above 8 tended to be malignant. A significant correlation between SUVmax and maximal diameter of the thyroid incidentaloma was also indicated.

Conclusions: Thyroid incidentaloma detected by 18FFDG PET/CT has higher risk rate for thyroid malignancy; SUVmax can be used for differentiating benign from malignant thyroid tumors.